Temperature stable membrane plate structure for a loudspeaker

ABSTRACT

The present invention relates to a membrane plate structure for generating sound waves. The membrane plate structure comprises a first skin layer, a second skin layer, a foam core layer which is interposed between the first skin layer and the second skin layer, and two binding layers. At least one of the first skin layer and the second skin layer is attachable to a vibrating element for generating sound waves. The elastic modulus of the core layer and its density are lower than the elastic modulus and the density of the first skin layer and the second skin layer, so that a sandwich structure is achieved. The Young modulus and the shear modulus of first skin layer, the second skin layer, the core layer and the binding layers are not variating between each other of more than 30% between a temperature 20° C. and 150° C., particularly between 20° C. and 170° C., more particularly 20° C. and 180° C.

FIELD OF INVENTION

The present invention relates to a membrane plate structure forgenerating sound waves, to a loudspeaker comprising the membrane platestructure, to a handheld device, and to a method of manufacturing amembrane plate structure.

BACKGROUND

Loudspeaker, in particular in micro-speakers for portable devices(mobile phones), and more in particular receiver micro-speaker (alsocalled ear-pieces, responsible for the voice sound-transmission), needthinner elements in order to reduce the overall size of the loudspeaker.In general, a loudspeaker comprises a diaphragm which is excited by acoil or another vibrating element.

In US 2013/0016874 A1 for example this function is represented by theelement 121 of a diaphragm 12 which guarantees high break-up frequencyand low weight. This element is often called membrane plate, to bedistinguished from the surround (connecting area 123) which is oftencalled membrane. The characteristics required by a membrane plate are:

-   -   a. High material resonance frequency—to guarantee a linearity        and the absence of acoustic peaks in the hearable region    -   b. Low weight—to reduce the moved mass and consequently increase        the sound pressure level and the efficiency of the speaker    -   c. High temperature resistance—to guarantee the same mechanical        stiffness at higher working temperatures

The resonance frequency of a material is directly proportional to itslength and width and a figure of merit, here defined “Frequency Factor”.The frequency factor is defined as follow:

$d\sqrt{\frac{B}{\rho}}$

Where d, is the total thickness, B is the bending module, and ρ is thedensity of the membrane plate material. The square root is also thespeed of sound of the material.

In micro-speakers, due to very small available thickness, the membraneplates are generally designed with a total thickness lower than 500 μm.

For these applications, due to the low available thickness, in order toachieve high frequency factors, it is necessary to utilize highmechanical performance materials. Sandwich constructions represent asolution for this application, since they offer a proper ratio ofbending module to weight (see also “An Introduction to SandwichConstruction”, Zenkert, D., 1995, Engineering Materials AdvisoryServices Ltd).

In micro-speaker applications, the actual state of the art is disclosedfor example in CN 204707266 U.

SUMMARY OF THE INVENTION

There may be a need to provide a component for a loudspeaker with verysmall space requirements and a high temperature resistance or stability.

According to an embodiment of the present invention, a membranestructure for generating sound waves is presented. The membrane platestructure comprises a first skin layer, a second skin layer, a foam corelayer which is interposed between the first skin layer and the secondskin layer and two binding layers interposed between the two skin layersand the core layer. For example, one of the skin layers is e.g.attachable to a coil or another vibrating element for generating soundwaves.

According to an embodiment of the present invention, the Young modulusand the density of the core layer are lower than the Young modulus andthe density of the first membrane skin layer and the second membraneskin layer, wherein the Young modulus and the shear modulus of all thelayers is not decreasing by more than 30% between 20° and 150° C.,preferably between 20° C. and 170° C., mostly preferably 20° C. and 180°C. In other words, the Young modulus and the shear modulus of first skinlayer, the second skin layer, the core layer and the binding layers maybe configured to not reduce their value of the Young modulus and theshear modulus of more than 30% between a temperature of 20° C. and 150°C.

According to another embodiment of the present invention, a microspeaker (in particular for a handheld device) is provided whichcomprises a membrane plate structure having the above mentionedfeatures.

According to still another embodiment of the present invention, ahandheld device (in particular a mobile phone) is provided whichcomprises at least one of a membrane plate structure having the abovementioned features and a micro speaker having the above mentionedfeatures.

According to yet another embodiment of the present invention, a methodof producing a membrane plate structure is provided, wherein the methodcomprises providing a first skin layer, providing a second skin layer,interposing a foam core layer between the first skin layer and thesecond skin layer, and arranging two binding layers between the foamcore layer and the skin layers. At least one of the first skin layer andthe second skin layer may be configured to be coupled to a vibratingelement for generating sound waves, the Young modulus of the core layermay be configured to be lower than the Young modulus of the first skinlayer and the second skin layer, the density of at least one of thefirst skin layer and the second skin layer may be configured to behigher than the density of the core layer, and the Young modulus and theshear modulus of the first skin layer, the second skin layer, the corelayer and the binding layers may be configured to change their value bynot more than 30% between a temperature of 20° C. and 150° C.

DESCRIPTION OF FURTHER EXEMPLARY EMBODIMENTS

According to a further embodiment of the present invention, the firstskin layer, the second skin layer, the binding layers and the core layerform a stack having a curved, in particular wavelike, or dish(trapezoid) like, or dome like, or conus like extension. In other words,the membrane plate structure comprises a curved, wavelike, or dished(trapezoid) like, or dome like or conus like structure and does not onlyextend within a plane. By the term “curved extension” it is meant inparticular, that the mentioned layers extend not completely within aplane. For example, a center of a layer is arranged within a first planeand an edge portion of the layer is arranged outside of the first plane(in particular within a second plane which is spaced apart from thefirst plane).

According to a further embodiment of the present invention, the shape isrealized with a forming procedure after the production of the sandwich,through the use of a cold or warm stamping process performed in atemperature range between 0° C. and 200° C., or a pressure formingprocess performed in a temperature range performed between 0° C. and200° C. Modern micro-speakers may use higher output power (1-3, 5 W) toincrease the loudness of the speaker. This power may cause very highcoil temperatures, which are also conveyed to mechanically relevantparts such as the membrane (or surround) and the membrane plate (ordiaphragm). Such temperatures can exceed 140° C.-150° C., up to 180° C.

Moreover, to achieve louder micro-speakers it may be necessary to reducethe moved mass, and a way to increase the stiffness to weight ratio ofthe diaphragm is to use a non planar geometry. Specifically, this isadvantageous for sandwich materials, especially with a sandwich withaluminum as skin layer which may be used according to an embodiment ofthe present invention.

By an embodiment of the present invention, the described sandwichmaterial is usable in a micro-speaker and fulfills the requirements inparticular regarding stiffness to weight ratio and heat resistance. Infact, by the described sandwich material its mechanical properties maybe maintained at temperatures up to e.g. 180° C. as at ambienttemperature and the material can be plastically formed into a non-planargeometry.

Advantages of using a high temperature-stable and plastic-formablematerial are:

-   -   Possibility of creating diaphragms with high break-up frequency        and total weight lower than 150 g/m²    -   Possibility to create materials with high temperature mechanical        stability (high HDT and flat DMA curves), and consequently the        possibility to obtain the same frequency response at cold state        and after some minutes of music reproduction (warm speaker).    -   Very easy, cheap and precise forming manufacturing (ex        stamping), suitable for mass-production.

As mentioned above, the micro speaker may be used within a handhelddevice, such as a tablet PC, smartphone, notebook computer and/or earphones.

The micro speaker comprises for example a carrier element, a coil whichis coupled to the carrier element by meaning of so-called surround ormembrane and a membrane plate structure coupled with the coil forgenerating sound waves.

According to an exemplary embodiment, a choice of ductile materials asskin layer and core layers may be made which allows the sandwich to beplastically formable or deformable (e.g. by cold and warm forming). Suchmaterials are ideally metals foils (especially aluminum) for skin layersand thermoplastic material as binding layer and core layers.

According to an exemplary embodiment, the core layer is a polymeric foamlike, but not only limited to, PMI (Polymethacrylimide) foam, polyesterfoams, polyurethane foams, polysulfone or polyethersulfone based foams,polyphenilene-sulfide foams, etc.

According to an exemplary embodiment, the first membrane skin layerand/or the second skin layer is made of metal foil or aluminum foil,with a thickness equal or lower than 15 μm (Micrometer) per layer.

According to an exemplary embodiment, the binding or bonding layers aremade of a thermoplastic material like polyolefins, polyesters,polyamides, silicones.

According to an exemplary embodiment, the bonding layers are made of anelastomer material like polyacrylates, rubbers etc. In this case, anadvantage would be to achieve higher damping factors at costs of lowerbending stiffness.

According to an exemplary embodiment, the bonding layers are made of athermoset material, like epoxy resins, polyester resins, polyurethans,polyimides.

According to an exemplary embodiment, the first skin layer, the secondskin layer and the core layer form a stack having an area density lowerthan 150 g/m².

According to an exemplary embodiment, the first skin layer, the secondskin layer and the core layer form a stack having a total thicknesslower than 500 μm.

According to an exemplary embodiment, the first skin layer, the secondskin layer and the core layer form a stack having a bending modulushigher than 5 GPa, in particular more than 10 GPa, further in particularmore than 15 GPa.

According to an exemplary embodiment, the first skin layer, the secondskin layer and the core layer form a non-planar structure having a totaldepth of less than ⅕, in particular 1/10, further in particular 1/20, ofa largest width of the stack. This geometry restriction is advantageousto achieve a formed structure through the stamping or pressure formingprocess with very thin skin layers. For example, the form of a conuswith a high ratio of depth to width will be difficult to achieve with astamping process.

According to an exemplary embodiment, the material can be producedthrough a cold lamination process.

According to an exemplary embodiment, the material can be producedthrough a lamination process, in particular at a temperature higher thanthe melting point of the bonding layers and lower than the melting pointof the core layer.

According to an exemplary embodiment, to facilitate the laminationprocess at lower temperatures, the thermoplastic bonding layer has amelting point lower than 210° C., in particular lower than 190° C., morein particular lower than 180° C.

According to an exemplary embodiment, the material can be produced withthe application of a resin on one skin layer, adding the foam layer,covering of the resin with second skin layer, and the curing of theresin.

It has to be noted that embodiments of the invention have been describedwith reference to different subject matters. In particular, someembodiments have been described with reference to apparatus type claimswhereas other embodiments have been described with reference to methodtype claims. However, a person skilled in the art will gather from theabove and the following description that, unless other notified, inaddition to any combination of features belonging to one type of subjectmatter also any combination between features relating to differentsubject matters, in particular between features of the apparatus typeclaims and features of the method type claims is considered as to bedisclosed with this application.

BRIEF DESCRIPTION OF THE DRAWINGS

The aspects defined above and further aspects of the present inventionare apparent from the examples of embodiment to be described hereinafterand are explained with reference to the examples of embodiment. Theinvention will be described in more detail hereinafter with reference toexamples of embodiment but to which the invention is not limited.

FIG. 1 shows a schematic view of a loudspeaker comprising a membraneplate structure according to an exemplary embodiment of the presentinvention, wherein the membrane plate structure comprises a flat shape.

FIG. 2 shows a schematic view of a loudspeaker comprising a membraneplate structure according to another exemplary embodiment of the presentinvention, wherein the membrane plate structure comprises a wavelikeshape.

FIG. 3 shows a dynamic mechanical analysis (DMA) for a conventionalmembrane plate structure and for a membrane plate structure according toan exemplary embodiment of the present invention.

FIG. 4 shows a handheld device with a micro speaker having a membraneplate structure according to an exemplary embodiment of the presentinvention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The illustrations in the drawings are schematic. It is noted that indifferent figures similar or identical elements are provided with thesame reference signs.

FIG. 1 shows a schematic view of a loudspeaker 110 comprising a membraneplate structure 100 according to an exemplary embodiment of the presentinvention. The loudspeaker 110 comprises a carrier element 104, a coil105 as vibrating element which is coupled to the carrier element 104 anda membrane plate structure 100. The membrane plate structure 100 issupported by the carrier element 104 such that the membrane platestructure 100 is excitable by the coil 105 for generating sound waves.

The membrane plate structure 100 for generating sound waves comprises afirst skin layer 101, a second skin layer 102, a foam core layer 103which is interposed between the first skin layer 101 and the second skinlayer 102, and two binding layers 106 between the foam core 103 and therespective skin layers 101, 102. At least one of the first skin layer101 and the second skin layer 102 is coupled to vibrating elementembodied as coil 105 for generating sound waves. The Young modulus ofthe core layer 103 is lower than the Young modulus of the first skinlayer 101 and the second skin layer 102. The density of the first skinlayer 101 and/or the second skin layer 102 is higher than the density ofthe core layer 103. The Young modulus and the shear modulus of the firstskin layer 101, the second skin layer 102, the core layer 103 and thebinding layers 106 are configured to not change or modify theirrespective value of the Young modulus and the shear modulus of more than30% between a temperature of 20° C. and 150° C. In other words, neitherthe Young modulus nor the shear modulus will change its respective valueby more than 30% in the event of a temperature change between 20° C. and150° C. for the materials of the first skin layer 101, the second skinlayer 102, the core layer 103 and the binding layers 106.

The coil 105 may be electrically excited by a control unit (not shown).The membrane plate structure 100 is coupled to the coil 105 such thatthe excited coil 105 excites the membrane plate structure 100 as well.The membrane plate structure 100 vibrates in an excited state andthereby generates acoustic sound.

The core layer 102 is formed with a lower Young modulus than thesurrounding skin layers 101, 102. Hence, the membrane plates 101, 102are stiffer than the core layer 103. This combination of layersgenerates efficient acoustic sound waves.

The membrane plate structure 100 according to the exemplary embodimentshown in FIG. 1 has a flat and uncurved design. The first skin layer101, the second skin layer 102, the binding layers 106 and the corelayer 103 form a stack extending within a plane. In other words, themembrane plate structure 100 has a flat, uncurved shape extending alongthe plane. More specifically, the first skin layer 100, the second skinlayer 102, the binding layers 106 and the core layer 103 extend alongrespective planes having parallel plane normals.

FIG. 2 shows another exemplary embodiment of a loudspeaker 110 havingcorresponding features as the loudspeaker 110 shown in FIG. 1, exceptthat the membrane plate structure 100 has a curved shape rather thanbeing planar. In particular, the first skin layer 101, the second skinlayer 102, the binding layers 106 and the core layer 103 form a stackhaving a curved, in particular wavelike, extension. In other words, themembrane plate structure 100 comprises a curved, wavelike structure andruns not within a plane.

FIG. 3 shows a diagram of a dynamic mechanical analysis (DMA)representing a relative E-Module (i.e. Young module) change with respectto respective temperatures.

Line 301 shows an E-Module change with respect to respectivetemperatures of a conventional membrane (ACR). The component loses mostof its shear modulus (e.g. E-Modulus) at a temperature of about 135° C.This means that if the speaker works at temperature higher than 135° C.,the break-up frequency of the speaker will be strongly reduced.

Line 302 represents a membrane plate structure 100 according to anexemplary embodiment (AXR). The membrane plate structure 100 maintainsthe Young modulus up to 180° C. with a loss lower than 30% compared tothe ambient temperature such as 20° C., allowing therefore the entirematerial to keep its bending modulus (e.g. relative E-Module) up to 180°C. with a loss lower than 30% compared to the ambient temperature's(around 20° C.) one. This property allows the speaker to reproduce thesound after some minutes of working almost as good as at ambienttemperature. Thus, the membrane plate structure 100 according to anexemplary embodiment shows a pronounced temperature resistance orstability.

FIG. 4 shows a handheld device 150, which is here embodied as a mobilephone, with a micro speaker type loudspeaker 110 having a membrane platestructure 100 (not shown) according to an exemplary embodiment of thepresent invention. Advantageously, the handheld device 150 can beoperated over a broad temperature range without deterioration of theloudspeaker's 110 sound quality.

It should be noted that the term “comprising” does not exclude otherelements or steps and “a” or “an” does not exclude a plurality. Alsoelements described in association with different embodiments may becombined. It should also be noted that reference signs in the claimsshould not be construed as limiting the scope of the claims.

LIST OF REFERENCE SIGNS

-   100 membrane plate-   101 first skin layer-   102 second skin layer-   103 core layer-   104 carrier element, membrane or surround-   105 coil-   106 binding layer-   110 loudspeaker-   150 handheld device

The invention claimed is:
 1. A method of producing a membrane platestructure, wherein the method comprises: providing a first skin layer;providing a second skin layer; interposing a foam core layer between thefirst skin layer and the second skin layer; arranging two binding layersbetween the foam core layer and the skin layers, wherein the first skinlayer, the second skin layer, the binding layers, and the core layerform a stack, wherein at least one of the first skin layer and thesecond skin layer is configured to be coupled to a vibrating element forgenerating sound waves; wherein the Young's modulus of the core layer isconfigured to be lower than the Young's modulus of the first skin layerand the second skin layer, wherein the density of at least one of thefirst skin layer and the second skin layer configured to be higher thanthe density of the core layer; and wherein the Young's modulus and theshear modulus of the first skin layer the second skin layer, the corelayer and the binding layers are configured to change their value by notmore than 30% between a temperature of 20° C. and 150° C., and whereinthe binding layers are structured to provide stiffness to the stack. 2.The method of claim 1, wherein the two binding layers consist of asubstantially similar material and wherein the two binding layersconsist of a material selected from the group of materials consisting ofa thermoplastic and an epoxy resin.
 3. The method of claim 1, whereinthe method comprises joining the first skin layer and the second skinlayer, the core foam layer, and the binding layers through a warmlamination procedure, with the binding layers being thermoplasticlayers.
 4. The method of claim 3, wherein a melting temperature of thebinding layers is lower than 180° C.
 5. The method of claim 1, whereinarranging two binding layers between the foam core layer and the skinlayers further comprises depositing resin on the first skin layer,adding the core layer, depositing resin on the core layer, covering theresin with the second skin layer, and curing the resin.
 6. The methodaccording to claim 1, wherein the method comprises adjusting anon-planar form of the membrane plate structure after fabrication of thestacked layers, as a first procedure, in a second procedure, through theuse of one of a stamping process or a pressure forming process, inparticular performed at a temperature between 0° C. and 200° C.
 7. Themethod according to claim 1, wherein the first skin layer, the secondskin layer, the binding layers, and the foam core layer form a stackhaving a bending modulus greater than 10 GPa.
 8. A method of producing amembrane plate structure, wherein the method comprises: providing afirst skin layer; providing a second skin layer, wherein at least one ofthe first skin layer and the second skin layer is configured to becoupled to a vibrating element for generating sound waves; disposing afoam core layer between the first skin layer and the second skin layer,wherein the Young's modulus of the core layer is lower than the Young'smodulus of the first skin layer and the second skin layer, and whereinthe density of at least one of the first skin layer and the second skinlayer is higher than the density of the foam core layer; and arrangingbinding layers between the foam core layer and the skin layers such thata stack is formed thereby, wherein the Young's modulus of the first skinlayer, the second skin layer, the core layer, and the binding layers areconfigured to change their value by not more than 30% between atemperature of 20° C. and 150° C., wherein a bending modulus of thestack is greater than 10 GPa, wherein the two binding layers areconstructed of a substantially similar material, and wherein the twobinding layers, as integrated into the stack, increase the stiffness ofthe stack.